The present invention relates to apparatus and methods for welding underwater and particularly relates to a two-stage dry chamber system for automatic underwater remote welding.
There are many environments in which welding must occur underwater. For example, nuclear reactor vessels contain water and the fuel bundles are maintained submerged. A nuclear reactor vessel typically has an interior stainless steel cladding overlying a low alloy carbon steel. In certain instances, the cladding is damaged exposing the low alloy carbon steel to the interior of the vessel. It is therefore necessary to apply a steel plate over the damaged area of the vessel and this operation is performed by welding the steel plate to the vessel in the underwater environment.
Generally, there are a number of different methods for maintaining welding apparatus dry while welding in an underwater environment. For example, a single chamber containing the welding unit may be utilized, the chamber being open at the bottom and sealed at the top. The chamber does not seal against the area to be welded but relies on trapped air in the chamber to maintain the welding unit dry. This however works only if the chamber can be lowered completely over the weld area such that the weld area is in a gaseous environment, e.g., atmospheric air or an inert gas, within the chamber. There are however various areas, for example, in a reactor vessel where the single chamber technique cannot be performed and generally the vessel has to be drained for repair. Accordingly there is a need for an underwater welding system which can be remotely actuated and perform welds generally without respect to the orientation of the weld area.